Reusable refractory molds usually made of graphite or the like are widely used with exothermic welding materials to make a wide variety of high ampacity low resistance electrical connections. Typical of such molds are those sold under the well-known trademark CADWELD.RTM. by ERICO International of Solon, Ohio USA.
Such reusable molds are two or more part molds usually opened and closed and held together by toggle clamps. The mold parts have faces which abut at a parting plane in which are formed recesses forming the various cavities and passages when the parts are clamped together. Typically the mold parts form a weld chamber, which usually includes a riser which may be the enlarged lower end of a tap hole passage which extends from the top of the mold to the weld chamber. The parts to be welded enter the weld chamber through sleeving passages which extend from outside the mold to the weld chamber. Such passages usually extend horizontally or from the bottom. Horizontal passages are typically employed when welding cable-to-cable. They may be used in combination with a vertical passage when welding cable to an earthing rod, for example.
A crucible normally sits on top of the assembled mold parts. The crucible includes a chamber holding the exothermic material on top of a fusible disc. A sprue or tap hole below the disc communicates with the top of the tap hole of the mold. When a measured and controlled quantity of exothermic material is ignited, it forms molten metal which fuses the disc permitting the molten metal to run downwardly into the weld chamber to weld any parts exposed to the chamber. Any slag forms on top of the weld metal and normally accumulates in the riser. After the weld cools, the mold is disassembled and any slag removed. The mold and crucible are cleaned for reuse.
Such molds can be rather intricate and are not insignificant in cost. The number of times a mold can be reused has a very direct impact on the cost of each weld connection. It has been found that the greatest wear on such molds occurs at the sleeving passages. This is particularly true where the sleeving passages accommodate stranded cable which may vary in size. With such cable, sealing material or packing must normally be employed to prevent the molten metal from leaking. Where the conductor is undersize the mold sleeving passage, adapter sleeves or shims around the conductors may be employed to fit the sleeving passage, and such may be used in combination with the packing material. All of the above adds to the cost of the weld.
Although it is always recommended to preheat the mold before use to ensure no moisture comes in contact with the molten metal, it can be seen that this is less of a problem if the weld chamber is not sealed, but well vented, especially along the sleeving passages.
For most connections, it is a time consuming job to locate the cable ends properly in the weld chamber beneath the tap hole, all properly sleeved, shimmed or sealed. Cable of considerable length and size is bulky and difficult to handle and keep in one place. This is particularly true where the operator is trying to close the mold parts properly on three cables or two cables and a ground rod, for example. Sometimes special cable clamps must be used. It would be very convenient if the operator could insert the cable ends into an already closed mold, and to a physical stop. It would also be convenient to have a mold system where the cable ends would stay where positioned as the operator proceeds with the welding operation. It can be seen that it would be highly advantageous to provide a mold system for electrical or earthing connections and the like which would readily accommodate different size cabling without the use of packing, adapter sleeves or shims and with minimal wear on the sleeving passages. It would also be desirable for the mold systems to maintain the weld chamber well vented to atmosphere.